It really depends on where you live. There are some parts of the world where environmental factors like ocean humidity or winter road salting will cause a car’s frame to rust through in a few years if you’re not careful. Look up the Rust Belt for an example.
On the other hand, if you live somewhere warm and dry, your car’s frame and body will outlast its original mechanical components.
“Rust Belt” isn’t literal, it refers to an area of the US where industrial manufacturing declined significant in the second half of the 20th century. It’s called that in part at least because its previous moniker was “Steel Belt”.
No that’s just proper maintenance… allowing salt to sit on the car constantly is not keeping up with maintenance.
Also as the other user has stated rust belt has nothing to do with cars rusting.